Fish Bait Sharks Have A Few Words To Say About New Fiber Optic Cables -- They`re Tasty.

June 13, 1987|The New York Times

NEW YORK -- Sharks have shown an inexplicable taste for the new fiber-optic cables that are being strung along the ocean floor linking the United States, Europe and Japan, telephone company officials say.

In the Atlantic alone, shark bites have caused the failure of four segments of cable, which is the main artery for global voice and computer communications. And British telephone officials monitoring the installation of the fiber-optic network that will link the United States to Japan and Guam are also reporting troubles with gnawing sharks.

The attacks have caused some delays in laying cable, and a single bite on a deep-sea line, which is about the size of a garden hose, can cost $250,000 or more to fix. There is a benefit, however. In studying ways to limit damage from the attacks, the telephone companies are providing marine scientists with valuable new data on sharks and specimens of previously unknown species.

The first evidence of sharks` attraction to the cables was the discovery of shark teeth embedded in an experimental line off the Canary Islands in 1985. A shark usually loses teeth when it bites something, and it later grows new ones.

``We were surprised,`` said James M. Barrett, deputy director of international engineering for the American Telephone and Telegraph Co. ``We had laid 55,000 or 60,000 miles of undersea cable all over the world with no problem. There had not been a single case of a shark biting one of the old (copper) cables.``

After further instances of having cables damaged by shark bites, AT&T officials now say they are confident that by wrapping the cable in double layers of steel tape they can prevent future damage. But the cause of the ``Jaws syndrome,`` as one telephone company spokesman called it, remains a mystery.

The fiber-optic cables look essentially the same as copper cables, except that the newer cables are less than an inch in diameter -- mere dental floss to a big shark -- while the older ones are as thick as an arm. Both also have armored jackets and contain copper wires that carry electrical power to amplifying stations along the way.

Inside each of the new cables, however, are six hairlike strands of glass that can carry as many as 40,000 separate conversations traveling as staccato pulses of laser light.

Construction of the trans-Atlantic fiber-optic network is scheduled to be completed in 1988. But the attacks on functioning segments of test lines in the Canary Islands are worrisome to AT&T and its several dozen foreign partners in the $1 billion projects.

Besides the potential to disrupt communications, the bites require repairs that often take a week or more, depending on depth and the weather.

Compared with the other hazards of the deep -- fishing lines, anchors and propellers, volcanoes, earthquakes and jagged ridges -- sharks would seem to be a minor threat to the cables. But the sharks` unpredictability and their sudden, unexplained interest in the fiber-optic lines prompted AT&T to support a study program involving dozens of people at several leading marine research centers.

Barrett said he believes a combination of factors may be responsible for the attacks, all of which have occurred about a mile deep on cable that was laid without slack. It is possible, he said, that vibrations of the taut cable occur at a frequency that sharks identify with food.

Also, some researchers believe there may be something unusual about the electrical current in the fiber-optic lines that attracts sharks and that may trigger an automatic feeding reflex.

Barrett said the fiber-optic cables would be armored to depths of 2,500 meters to protect against shark bites, and buried in trenches closer to shore to guard against fishing boat anchors.